1. Field of the Invention
The present invention relates to a semiconductor integrated circuit which switches a bit number of a digital signal.
2. Description of the Related Art
One of methods for a D/A converter is a dynamic element matching (hereinafter referred to as DEM) method (for example, disclosed in Japanese Unexamined Patent Application Publication No. 2000-168977). In the DEM method, by sequentially switching plural elements such as resistors within a predetermined period of time, dispersions in element characteristics can be suppressed to a minimum. On this occasion, a switch circuit to supply data values to the elements is configured using a barrel shifter or a shift register. Consequently, D/A conversion accuracy can be improved irrespective of relative dispersions in element characteristics. Further, there is a disclosed technique of improving the accuracy of the D/A converter by adding minute resistors in order to adjust resistance values of the resistors for D/A conversion (for example, Japanese Unexamined Patent Application Publication No. 2000-349641).
The above-described DEM D/A converter cancels dispersions in element characteristics by cyclically shifting the data values supplied to the elements according to a predetermined rule by the switch circuit. Namely, the elements for D/A conversion are used cyclically according to a predetermined rule. Consequently, the accuracy of the D/A converter can be improved as compared with methods in which DEM is not used. However, on the other hand, the switch circuit can perform only a cyclic shift operation, so that the accuracy of the D/A converter changes cyclically within a predetermined period of time.